1. Field of the Invention
The present invention relates to a guide mechanism for guiding a pickup. For example, the present invention relates to a guide mechanism for guiding a pickup with respect to an information recording face of an optical disk when it is applied to an optical disk reproducing device or an optical disk recording device.
2. Description of the Related Art
Conventionally, an optical disk reproducing device such as a CD player is capable of accurately reading information recorded on a CD as follows. When the CD on which a row of pits having information are spirally recorded is rotated by a spindle motor, the row of pits form a track of information to be scanned. While the track of information is accurately followed in the radial direction of the disk by a pickup attached to a pickup guide mechanism fixed to a casing of the CD player, the row of pits to be scanned can be optically read in order. In this way, information recorded on the CD can be read.
FIG. 4 is a view showing the above conventional pickup guide mechanism. On the chassis 101 of the pickup guide mechanism 100, there is provided a shaft presser 103 to which a rod-shaped guide shaft 102, the rigidity of which is high, is attached. When a recessed portion of the shaft presser 103 comes into contact with one end portion of the guide shaft 102, the guide shaft 102 can be positioned, and also when the other end portion of the guide shaft 102 is fixed by a countersunk head screw 104 screwed into a screw hole formed on the chassis 101, the guide shaft 102 can be arranged over an opening formed on the chassis, so that the guide shaft 102 can be positioned in the radial direction of a disk, that is, the guide shaft 102 can be positioned in the direction of arrow A. In this way, the guide shaft 102 can be fixed at a predetermined position shown in FIG. 4.
For example, as shown in FIG. 4, the shaft presser 103 is made of resin by means of molding, and the bottom portion of the shaft presser 103 is fixed onto the chassis 101. Alternatively, the shaft presser 103 may be formed by raising a portion of the chassis 101.
A pickup 105 is slidably supported by the guide shaft 102. When a drive force of a carriage motor 106 is transmitted to a rack 108, which is fixed to the pickup 105, via a gear 107, an objective lens 109 of the pickup 105 can be moved in the radial direction of the disk.
FIG. 5 is a view showing the guide shaft 102 fixed onto the chassis 101 by the countersunk head screw 104. The profile of the head portion of the countersunk head screw 104 is formed into a substantial cone shape having a tapered face. Taper angle xcex8 of the tapered face of the head portion of the countersunk head screw 104 is 90xc2x0 by the standard size according to JIS (Japanese Industrial Standard), and the allowance does not exceed 90xc2x0.
The central axis of the countersunk head screw 104, which is screwed to the chassis 101, is located at a predetermined position on central axis X of the guide shaft 102 as shown in FIG. 4, and the central axis of the countersunk head screw 104 makes a right angle with central axis X of the guide shaft 102.
Therefore, when the countersunk head screw 104 is screwed to the chassis 101, the highest portion of one end of the guide shaft 102 comes into contact with an inclined face (tapered face) of the head portion of the countersunk head screw 104 forming angle xcex8. Therefore, the highest portion of one end of the guide shaft 102 is pushed by force F of the tapered face. In this case, force F of the tapered face is perpendicular to the tapered face.
Component force Fz of force F, the direction of which is vertical, fastens one end portion of the guide shaft 102 by the countersunk head screw 104 and the chassis 101, so that the guide shaft 102 can be fixed onto the chassis 101 by this fastening force Fz. Component force Fxy of force F, the direction of which is horizontal, pushes the other end portion of the guide shaft 102 against the shaft presser 103, so that the guide shaft 102 can be positioned in the radial direction of the disk by this component force Fxy of force F.
In this case, as can be seen in FIG. 5, an angle formed between force F, which is perpendicular to the tapered face, and component force Fxy, which is horizontal, is xcex8/2. Accordingly, for example, when angle xcex8 of the head portion of the countersunk head screw 104 is a standard size (90xc2x0), the angle formed between force F, which is perpendicular to the tapered face, and component force Fxy, which is horizontal, becomes 45xc2x0. Therefore, the intensity of component force Fz and that of component force Fxy become equal to each other.
In the case where angle xcex8 of the head portion of the countersunk head screw 104 is formed in an allowance which deviates from the standard size, the angle formed between force F, which is perpendicular to the tapered face, and component force Fxy, which is horizontal, becomes smaller than 45xc2x0. In this case, an intensity of component force Fxy becomes a little lower than that of component force Fz.
When the guide shaft 102 receives this fastening force Fz and this pushing force Fxy, it can be fixed to a predetermined position on the chassis 101.
When it is estimated that the CD player on which the pickup guide mechanism is mounted is incorporated into a vehicle or used as a portable CD player, it is necessary to give a sufficiently high intensity of fastening force so that the guide shaft 102 can not be easily disconnected from the chassis 101 even if it is given external vibration or shock caused when the CD player is carelessly dropped.
In this connection, as described before, since angle xcex8 of the head portion of the countersunk head screw 104 is 90xc2x0, the intensity of component force Fz and that of that of component force Fxy necessarily become equal to each other. Therefore, when the countersunk head screw 104 is screwed into the chassis 101 so as to provide a sufficiently high fastening force, the pushing force is also increased.
When the pushing force is increased, a load given to the shaft presser 103 is also increased. Therefore, it is impossible for the shaft presser 103 to withstand the load, and the shaft presser 103 is plastically deformed. FIG. 6 is a view showing a state in which the shaft presser 103 is deformed as described above.
As shown in FIG. 6, when one end portion of the guide shaft 102 is pushed by force Fxe2x80x2, which is sufficiently higher than force F, by the inclined face of the head of the countersunk head screw 104, pushing force Fxe2x80x2xy, which is sufficiently higher than pushing force Fxy, of a component force of force Fxe2x80x2 is generated, and also pushing force Fxe2x80x2z, which is sufficiently higher than pushing force Fz, of a component force of force Fxe2x80x2 is generated.
As a result, the guide shaft 102 pushes the shaft presser 103 by pushing force Fxe2x80x2xy. However, the shaft presser 103 can not withstand this pushing force Fxe2x80x2xy. Therefore, the guide presser 103 is deformed being pushed by the guide shaft 102. At the same time, the guide shaft 102 is pushed in the thrust direction by the inclined face of the head portion of the countersunk head screw 104 which gradually proceeds downward being screwed into the chassis 101. As a result, the guide shaft 102 deviates from a predetermined position.
As a result, not only the shaft presser 103 of the pickup guide mechanism is damaged but also the chassis 101 is deformed under certain circumstances, and it becomes impossible for the guide shaft 102 to be stably fixed at the predetermined position on the chassis 101.
For the above reasons, in the conventional pickup guide mechanism, only pushing force Fxy, the intensity of which is kept in a range by which the shaft presser 103 is not deformed, can be given to the guide shaft 102. As a result, it is impossible for the guide shaft 102 to be fixed onto the chassis 101 by a sufficiently high intensity of force Fz. Accordingly, there is a limitation in increasing the mechanical strength of the pickup guide mechanism so that it can withstand the vibration and shock given from the outside.
The present invention has been made in view of the above problems. It is an object of the present invention to provide a pickup guide mechanism, the guide shaft of the pickup of which can be stably fixed at a predetermined position on the chassis by a sufficiently high intensity of fastening force, so that the pickup guide mechanism can withstand vibration and shock given from the outside.
In order to achieve the above object, according to a first aspect of the invention, there is provided a pickup guide mechanism comprising: a shaft for guiding a pickup over an opening formed on a chassis; and fixing means for fixing the shaft to the chassis, the fixing means including a countersunk head screw, which is screwed to the chassis, a tapered face of a head portion of which pushes an end portion of the guide shaft, wherein the taper angle of the tapered face of the head portion exceeds 90xc2x0.
Due to the foregoing, by the pushing force of the tapered face of the head portion of the countersunk head screw which pushes one end portion of the guide shaft, it is possible to obtain a component force (pushing force) by which one end portion of the guide shaft is pushed in the horizontal direction of the fixing means so that no play is created in the guide shaft. Further, it is possible to increase an intensity of the component force (fastening force) for fixing the guide shaft to the chassis by fastening the guide shaft with the countersunk head screw and the chassis as compared with an intensity of the pushing force. Therefore, the guide shaft can be stably positioned by the pushing force without causing any play, and further the guide shaft can be fixed to the chassis by a sufficiently high intensity of fastening force. As a result, the pickup guide mechanism can be stably fixed at a predetermined position on the chassis while a sufficiently high intensity of fastening force is given to the guide shaft without causing any damage in each portion of the pickup guide mechanism.
According to a second aspect of the invention, there is provided a pickup guide mechanism comprising: a shaft for guiding a pickup over an opening formed on a chassis; and fixing means for fixing the shaft to the chassis, the fixing means including a presser section, which is arranged on the chassis, coming into contact with one end portion of the guide shaft and positioning the guide shaft, and a countersunk head screw, which is screwed to the chassis, a tapered face of a head portion of which pushes the other end portion of the guide shaft toward the presser section, wherein the taper angle of the tapered face of the head portion exceeds 90xc2x0.
Due to the foregoing, by the pushing force of the tapered face of the head portion of the countersunk head screw which pushes one end portion of the guide shaft, it is possible to obtain a component force (pushing force) by which one end portion of the guide shaft of the fixing means is pushed in the horizontal direction so that no play is created in the guide shaft. Further, it is possible to increase an intensity of the component force (fastening force) for fixing the guide shaft to the chassis by fastening the guide shaft with the countersunk head screw and the chassis as compared with an intensity of the pushing force. Therefore, the guide shaft can be stably positioned by the pushing force without causing any play, and further the guide shaft can be fixed to the chassis by a sufficiently high intensity of fastening force. As a result, the pickup guide mechanism can be stably fixed at a predetermined position on the chassis while a sufficiently high intensity of fastening force is given to the guide shaft without causing any damage in each portion of the pickup guide mechanism.